More UI messages fixes...

git-svn-id: https://svn.blender.org/svnroot/bf-blender/trunk/blender@54940 954f8c5b-7b00-dc11-b283-0030488c597c
Fix #34414: python error with frame_change callback and Cycles motion blur.
Now the RenderEngine.render callback allows writing blender data again, it
should not be allowed but in practice the API and render threading code is
too limited to make this work at the moment.

git-svn-id: https://svn.blender.org/svnroot/bf-blender/trunk/blender@54941 954f8c5b-7b00-dc11-b283-0030488c597c
Fix #34390: quicktime video codec menu showing blank. It's a small miracle
that this code worked at all at some point.

git-svn-id: https://svn.blender.org/svnroot/bf-blender/trunk/blender@54942 954f8c5b-7b00-dc11-b283-0030488c597c